I think the 'root rake' feature is nice at 72", but I really don't think a grapple has to be that wide to be VERY effective. Sometimes the width can be an annoyance because on uneven terrain, you may not be able to grab something without repositioning or dragging the object. However, I use my rock bucket grapple's finger tines to spread and smooth dirt & gravel much like a rake. You'll be able to do the same with that root grapple.
I think the weight of your grapple is fine. My root rake grapple weighs almost 800 lb and it sticks out way beyond where your grapple does. Most of your weight is very close to your loader arms so you have much more usable lift. Besides, in reality with a grapple, you don't always get the darn thing full with each load. Mostly, it's just how fast you can grab and move stuff without having to get off the tractor. I just grab what I can and save the rest for the next load. I can do in a couple of hours what it would take a month to do by hand. That's the value of a grapple. Since yours is heavy duty, you will do less damage to it no matter how hard you work. You found that out when you hit a rock. To me, a root rake/grapple with vertical teeth needs to be tougher than a bucket type debris grapple with horizontal tines. If your tractor can lift 1800 lb and the grapple weighs 800, you still have a massive payload capability.
EDIT: I forgot to say that I didn't load my rear tires until I got a rock rake grapple. It convinced me in a hurry to load them and always ensure I also had a heavy boxblade on the rear 3PH.
